Now, if the nuclear mass of an isotope is not given, then more extensive calculations will be needed to calculate the mass defect. Here we're going to say in these instances, nuclear mass is the difference between the mass number of the isotope and the mass of all of its electrons.
Now here we'd say that our nuclear mass equation is nuclear mass, which again is the atomic mass of the isotope equals its mass number minus the number of electrons times their individual atomic mass units. Remember, for electrons that's equal to 0.00055.
So this is the equation we utilize if we have to calculate nuclear mass on by ourselves, and it's not given to us within the question. So keep this equation in mind when looking for nuclear mass.
nuclear mass = mass number - number of electrons × 0.00055